Reproduction in Domestic Animals

Postpartum Ovarian Activity in South Asian Zebu Cattle 209(Abeygunawardena et al. 1992). The results were evenbetter (75% ovulation) when GnRH was injected on theday of lowest vaginal impedance (Sahu et al. 2005a)which normally happens under oestrogen influence,again suggesting the presence of active follicles in suchcases. Administration of GnRH in Gir cows just beforeAI reduced early embryonic mortality and enhancedpregnancy rates by 20%. The concentration of circulatingprogesterone on days 0, 14 and 22 post-treatment,however, was similar to the untreated controls (0.73 vs0.86; 9.92 vs 10.78 and 16.28 vs 14.72 nM, respectively;Shelar et al. 2002)Application of progestogens, more often in the formof norgestomet ear implants (CrestarÒ, Intervet, Holland)embedded subcutaneously for 9–12 days in zebucattle yielded variable results. Approximately 35% and60% cows manifested synergistic sexual behaviourbetween 31 and 57 days after norgestomet implantremoval in dry and wet seasons, respectively (Medranoet al. 1996). Singh et al. (2002) reported oestrousresponses in approximately 71% zebu cows with overallconception rate of up to 83%. Ovulatory oestrus hasalso been reported in 90% Deoni cows with conceptionrate of 70% with 1.85 services per conception (Markendeyaand Bharkad 2004). Solano et al. (2001),however, could achieve ovulations in only 16% Bosindicus cows following norgestomet implants alone.Oestrogen administered along with norgestomet implantsincreased the expression of behavioural oestrusbut had no bearing on ovulation rate. Incorporation ofequine chorionic gonadotropin (eCG) to progestogentherapy induced oestrus in 100% anoestrous zebu cattlewith good BCS (Abeygunawardena et al. 1992).Kathiresan et al. (2001) advocated two simultaneousnorgestomet implants instead of one in Kangeyam cows.While one implant increased LH pulsatile release andmaintained the dominant follicle, two implants suppressedLH release with pattern akin to a mid-lutealphase and restored dominant follicle turn over whichwas useful for oestrous synchronization. Oestrus couldalso be synchronized in cycling zebu with two PGF 2µinjections 11 days apart. Serum progesterone profileshowed that 67% and 100% of the animals responded tothe first and the second injection, respectively (Obasi etal. 1999). Ovsynch oestrous synchronization protocol,which proved meritorious in European breeds, performedpoorly in zebu (Baruselli et al. 2004) but proveduseful in inducing ovarian cyclicity in some anoestrousBos taurus · Bos indicus crosses under tropical conditions(Ahuja and Montiel 2004).Zebu cows respond well to superovulatory protocolsbeing used in European cows. Treatment with FSH as acomponent of the superovulatory protocols generated11.62 ± 1.28 ovulations and recovered 6.25 ± 2.63embryos of which, 2.35 ± 0.96 were viable and transferable.Finally, the subsequent calving rate in the implantedrecipient cows was 27.28% (Chakurkar et al. 2004).Although the results from the use of the aforesaidhormonal regimes were encouraging, yet their adoptionremained minimal. Under field conditions in Asia, zebucattle are generally reared at zero input system. Poor basaldiet, BCS and general management normally prevalentunder these circumstances are bound to affect overallreproductive performance of the cattle. Besides, highcosts of hormonal interventions is a deterrent. This alongwith lack of interest in promotion of indigenous zebucows could be the cause of lack of any proved superovulationand embryo transfer programme in zebu cattle.Managemental Aspects of the Onset ofPostpartum Ovarian ActivityQuality of management of animals affects postpartumreproduction in all species of animals, and so is in zebu.Oestrous detection was missed once or several times in34.7% of the cows, most likely because of poor oestrousdetection system or high incidence of silent oestrus(Lyimo et al. 2004). Oestrous detection is even worst inzebu cows reared by nomads and kept on free grazingpastures. Prevalence of a strong phenomenon of hierarchyin zebu cattle may also affect oestrous expressionand mating in subordinate cows (Solano et al. 2004).Body weight, heart girth and height at withers play asignificant role in determining social ranks among Rathicows. Dominance ranks have also been positivelycorrelated (p < 0.05) to lactation yield (Prasad et al.1996). Environmental extremes, especially the summer,are stressful to zebu cows. Scorching sun restrictsgrazing, thereby affecting body condition and ultimatelyovarian activity (Mitloehner and Laube 2003), cowslower in social ranking being more vulnerable.Long-term exposure of Bos indicus to heat stress haddeleterious effects on follicular dynamics and oocytecompetence (de S Torres-Ju´nior et al. 2008). Provisionof appropriate shade and cooling practices can beemployed to decrease effects of heat stress in cattle(Nienaber and Hahn 2007).Dynamics of body weight at calving, and thereforenutritional status, have great bearing on postpartumovarian activity in zebu. Early gain in body weightpostpartum was associated with early resumption ofovarian activity in Gir cows (Patil and Deshpande1981). Nutritional deficiency, especially during latepregnancy and early postpartum period, results in majorloss of body weight and prolonged postpartum anoestrusin zebu cattle (Montiel and Ahuja 2005). Supplementaryfeeding of UMMB to small zebu cows ofBangladesh initiated ovarian cyclicity by25.50 ± 3.39 days postpartum when compared with>60 days in the control group (Ghosh et al. 1993).Similar observations have been reported followingUMMB supplementation in several other South Asiancountries (Boettcher 2007). Supplementary feeding oftrace minerals and vitamin E for a period of 2 weeksinduced oestrus within 10 days in 65% anoestrousDeoni cows and all conceived to 1.9 services perconception (Markandeya et al. 2002).There is a strong bull effect on postpartum fertility,especially in feed-supplemented zebu cows. Exposure tobulls shortened the average length of postpartumanoestrus in zebu cattle from 119 to 95 days. Nutritionalsupplementation to these further helped their fertility.All such cows exhibited oestrus within 150 days postpartumagainst only 69% controls (Rekwot et al. 2004).Suckling is known to suppress postpartum fertility inmost species of mammals and is commonly practiced inÓ 2008 The Authors. Journal compilation Ó 2008 Blackwell Verlag